THE XBBVOUS SYSTEM
The flocculus is small, consisting of a mnifuer of siu/aii folia surrounding the auditory nerve. The para is large and composed of three partsódorsal, r and ventral, which are known respectively as the paraflocculus, petrosal lobule and ventral para: In the higher Apes this region diminishes in size, and the petrosal lobule vanishes. Another important .iirfe> ence between the brain in the Gibbon and those in rh*r higher Apes is seen in the pontine region. The trapezium which is exposed in the Cercopithecida? and bnriei in the higher Apes is hardly covered in the Gibbon*.
THE BRAIX ix THE OKAXG -fig. 50;.
The brain is more voluminous than that in the Gibbons, and its surface is more convoluted and fissured. When viewed from above it presents an oval outline, and when seen from below the excavations and keel on the frontal lobes are marked features.
The keel is slightly larger than in other Apes. The central sulcus (C.S.) has a genu. Superiorly it rarely passes on to the mesial surface of the brain, but it may be continued below by a shallow groove into the Sylvian fissure.
The superior frontal (S.F.S.) and superior pre-central sulci (S.P.S.) are united to form a triradius ; and there is a variable number of small middle frontal sulci (M.F.S.) between the superior frontal and inferior frontal (S JR.) sulci. The latter, or sulcus rectus, varies in development in different brains, and it unites behind with the triradiate inferior precentral sulcus, or sulcus arcuatus (I.P.S.). The sulcus arcuatus is sometimes connected to the Sylvian fissure by an inferior transverse